Selective rendering method and system for rapid 3 dimensional imaging

ABSTRACT

A method and system for selectively rendering a two dimensional view of a three dimensional image, in order to facilitate rapid three dimensional imaging in a realtime or static context. Specifically, the system includes means for identifying display coordinates that continue to show the same image coordinates from view to view, and bypasses rasterization for the next view for such display coordinates, thereby reducing the access to memory required in order to retrieve image data, as well as data processing time, all required to generate new two dimensional views of a three dimensional image.

FIELD OF THE INVENTION

The present invention relates generally to computer-generated images,and more particularly to a method and system for rapidly renderingsuccessive views in a series of views of a three dimensional image.

BACKGROUND OF THE INVENTION

Computer-generated images are used in many different industries to modelsurfaces and solids. In the medical fields, computer imaging is used incombination with ultrasound imaging, magnetic resonance imaging or othermedical imaging technology to display, analyze and organize the datathese medical imaging technologies provide. For example, ultrasoundmachines use ultrasonic wave, i.e. sonar, to scan a patient's body. Thedata thus obtained is then analyzed by physicians to assist thephysicians in their diagnosis and treatment of patients. Ultrasound canbe used to view a fetus, blood-flow patterns in arteries, or to scanorgans for irregularities such as cysts, etc.

Typically, a three dimensional image is displayed to a user by beingprojected on a two dimensional surface such as a screen. Again, thethree dimensional image is typically viewed by a user through a seriesof two dimensional Views to create a three dimensional image. As eachview is followed by the next view on the monitor, the displaycoordinates of the monitor are updated to display new image properties,which, in the aggregate, display the new two dimensional view.

This new two dimensional view may be the result of changes in a dynamicimage data set, such as when the view is being generated in realtime,while the data is being captured. Alternatively, the data set may bedynamic due to being downloaded from another source. Where the data setis static, such as when image data that has previously been acquired isbeing viewed, new views can be selected by geometrically manipulatingcoordinate space on which the static data set is mapped.

In realtime three dimensional rendering, the data set being rendered isa dynamic entity that changes with time as the data set is beingacquired. For example, capturing a monochrome ultrasound CINE clippedwith 150 frames, of typical dimension 640 by 480, the frame capture ratebeing 30 frames per second, requires an amount of memory equal to 150 by640 by 480 bytes to be reserved. These bytes are filled with a singleframe of data every one thirtieth of a second, until all 150 frames havebeen filled, which will take 5 seconds given a frame capture rate of 30frames per second.

In realtime three dimensional imaging, a static view of the data set istypically selected, and then updated as data is added to the data set.Various rendering techniques can be used such as three dimensionaltexture mapping, maximum intensity projection, opacity rendering orsurface rendering As data is added to the data set, and is subsequentlymapped to the coordinate space, some of this new data will be projectedonto the monitor. This will require the display coordinates on whichthis new data is projected to be rendered.

Rendering requires the data processor to access memory in order toobtain the necessary image data from the data set. Obtaining informationfrom memory represents a bottleneck in processing time, as theprocessors must wait for the information to be obtained from memory.Accordingly, rasterizing is both computationally intensive andcomparatively time-consuming.

These problems may also be present where the data set is a staticentity, and it is the view that is dynamic. Specifically, whenever theview is changed, it will be necessary to access memory in order toretrieve the image data required to rasterize the display coordinates ofthe monitor in order to be able to display the new view.

Accordingly, there is a need for a system and method of reducing thecomputation, as well as the access to memory, required to replaceexisting two dimensional views shown on a monitor, with now twodimensional views of the three dimensional data set.

BRIEF SUMMARY OF THE INVENTION

An object of one aspect of the present invention is to provide a methodand system for selective rendering and rapid three dimensional imaging.

In accordance with one aspect of the present invention, there isprovided a method for updating a display from an n^(th) view of a seriesof views of a three dimensional image to an (n+1)^(th) view of theseries of views of the three dimensional image. The three dimensional isgenerated in an image coordinate set of a coordinate space, and eachimage coordinate in the image coordinate set has an associated imageproperty. The image coordinate set includes, for the n^(th) view of theseries of views, an associated n^(th) image coordinate subset.

The display has a display coordinate set. The display coordinate set hasfor the n^(th) view of the series of views, an associated n^(th) displaycoordinate subset. The n^(th) view of the series of views is generatedby projecting the associated n^(th) image coordinate subset onto then^(th) display coordinate subset on the display so that each displaycoordinate in the n^(th) display coordinate subset has an associatedn^(th) view-specific image coordinate projected thereon. The (n+1)^(th)view of the series of views is generated by projecting the associated(n+1)^(th) image coordinate subset onto the (n+1)^(th) displaycoordinate subset on the display so that each display coordinate in the(n+1)^(th) display coordinate subset has an associated (n+1)^(th)view-specific image coordinate projected thereon.

The method includes the following steps:

(1) for each display coordinate in both the n^(th) display coordinatesubset and the (n+1)^(th) display coordinate subset,

(a) determining whether the n^(th) view-specific image coordinate is thesame as the (n+1)^(th) view-specific image coordinate; and,

(b) when the n^(th) view-specific image coordinate is the same as the(n+1)^(th) view-specific image coordinate, retaining the projection ofthe n^(th) view-specific image coordinate onto such display coordinateas the projection of the (n+1)^(th) view-specific image coordinate ontosuch display coordinate; and,

(b) when the n^(th) view associated image coordinate is different fromthe (n+1)^(th) view associated image coordinate, projecting the(n+1)^(th) view associated image coordinate onto such displaycoordinate.

Preferably, the method comprises adding an additional image coordinatesubset to the image coordinate set in an incremental time between thedisplay of the n^(th) view of the series of views and the (n+1)^(th)view of the series of views of the three dimensional image. The(n+1)^(th) view specific subset of the image coordinate set intersectswith the additional image coordinate subset. Preferably, the threedimensional image is being generated in real time by scanning an imagedobject. Alternatively, the image coordinate set is fixed and the(n+1)^(th) view of the series of views is generated by selecting the(n+1)^(th) view-specific subset of the image coordinate set.

In accordance with another preferred aspect of the invention, there isprovided a method of updating a display from a preceding view in twosuccessive views in a series of views of a three dimensional image to asubsequent view in the two successive views in the series of views ofthe three dimensional image. The three dimensional image is generated inan image coordinate set of a coordinate space. Each image coordinate inthe image coordinate set has an associated image property.

The display includes a display coordinate set and the preceding view isgenerated by a preceding projection of a preceding view image coordinatesubset of the image coordinate set onto a preceding view displaycoordinate subset of the display coordinate set so that each displaycoordinate in the preceding view image coordinate subset has anassociated preceding view image coordinate in the preceding view imagecoordinate subset projected thereon. The subsequent view is generated bya subsequent projection of a subsequent view image coordinate subset ofthe image coordinate set onto a subsequent view display coordinatesubset of the display coordinate set so that each display coordinate inthe subsequent view image coordinate subset has an associated subsequentview image coordinate in the subsequent view image coordinate subsetprojected thereon.

The method includes the following steps:

(1) for each display coordinate in both the preceding view displaycoordinate subset and the subsequent view display coordinate subset,

(a) determining whether the associated preceding view image coordinateis the associated subsequent view image coordinate;

(b) when the associated preceding view image coordinate is theassociated subsequent view image coordinate, retaining the precedingprojection of the associated preceding view image coordinate onto suchdisplay coordinate as the subsequent projection of the associatedsubsequent view image coordinate onto such display coordinate;

(c) when the associated preceding view image coordinate is not theassociated subsequent view image coordinate, stopping the precedingprojection of the associated preceding view image coordinate onto suchdisplay coordinate and beginning the subsequent projection of theassociated subsequent view image coordinate onto such displaycoordinate.

Preferably, the two successive views in the series of views of the threedimensional image are any two successive views in the series of views ofthe three dimensional image. Preferably, in an incremental time betweenthe display of the preceding view and the subsequent view, the imagecoordinate set of the coordinate space increases as an additional imagecoordinate subset is added to the image coordinate set. The subsequentview subset of the image coordinate set intersects with the additionalimage coordinate subset.

In accordance with a preferred aspect of the above-described method, thethree dimensional image is being generated in real time by scanning animaged object. Alternatively, the image coordinate set is static and thesubsequent view subset is selected from the static image coordinate set.

In accordance with a preferred embodiment of the invention, there isprovided a system for updating a display from a preceding view in twosuccessive views in a series of views of a three dimensional image to asubsequent view in the two successive views in the series of views ofthe three dimensional image The three dimensional image is generated inan image coordinate set of a coordinate space. Each image coordinate inthe image coordinate set has an associated image property. The displayhas a display coordinate set and the preceding view is generated by apreceding projection of a preceding view image coordinate subset of theimage coordinate set onto a preceding view display coordinate subset ofthe display coordinate set so that each display coordinate in thepreceding view image coordinate subset has an associated preceding viewimage coordinate in the preceding view image coordinate subset projectedthereon. The subsequent view is generated by a subsequent projection ofa subsequent view image coordinate subset of the image coordinate setonto a subsequent view display coordinate subset of the displaycoordinate set so that each display coordinate in the subsequent viewimage coordinate subset has an associated subsequent view imagecoordinate in the subsequent view image coordinate subset projectedthereon.

The system includes a determining means, a retaining means, and astopping means wherein for each display coordinate in both the precedingview display coordinate subset and the subsequent view displaycoordinate subset,

(1) the determining means determines whether the associated precedingview image coordinate is the associated subsequent view imagecoordinate;

(2) when the associated preceding view image coordinate is theassociated subsequent view image coordinate, the retaining means retainsthe preceding projection of the associated preceding view imagecoordinate onto such display coordinate as the subsequent projection ofthe associated subsequent view image coordinate onto such displaycoordinate;

(3) when the associated preceding view image coordinate is not theassociated subsequent view image coordinate, the stopping means stopsthe preceding projection of the associated preceding view imagecoordinate onto such display coordinate and beginning the subsequentprojection of the associated subsequent view image coordinate onto suchdisplay coordinate.

Preferably the two successive views in the series of views of the threedimensional image can be any two successive views in the series of viewsof the three dimensional image.

Preferably, the system includes a data update means for increasing theimage coordinate set of the coordinate space by adding an additionalimage coordinate subset to the image coordinate set during anincremental time between the display of the preceding view and thesubsequent view. The subsequent view subset of the image coordinate setintersects with the additional image coordinate subset. Preferably, thesystem comprises scanning means for generating the three dimensionalimage by scanning an imaged object.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made, by way of example, to the accompanyingdrawings which show preferred aspects of the present invention, and inwhich

FIG. 1 is a block diagram showing a selective rendering system for rapidthree dimensional imaging in accordance with an aspect of the presentinvention, and,

FIG. 2 is a listing of the logic steps to be executed in a selectiverendering method for rapid three dimensional imaging in accordance withan aspect of the present invention in which new frames of image data arebeing captured.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Referring to FIG. 1 there is illustrated a block diagram of a computersystem 22 for analyzing computer-generated three dimensional images inaccordance with a preferred embodiment of the invention. As shown inFIG. 1, the computer 22 is connected to a monitor 24 having a 640 by 480screen, an input device 30 such as a manually operated mouse 30, and anultrasound scanner 32.

When scanning a patient, an ultrasound operator passes a probe over aportion of the patient's body. The probe emits and receives a series ofultrasonic waves. Based on the difference between the ultrasonic wavesthat are emitted and those that are received, a frame of datarepresenting a cross-sectional view of the patient's body is obtainedalong the path of the probe. The probes generates, say, 150 frames ofdata in a typical pass over the scanned portion of the patient's body.Each frame of data represents a cross-section of the part of thepatient's body that is scanned using ultrasonic waves. Each frame istypically 640 by 480 pixels, but only the region of interest, which istypically about 250 by 250 pixels, is stored. Accordingly, the imagedata in the ultrasound scanner 32 for a single image would consist ofabout 150 frames, each frame being about 250 by 250 pixels.

The ultrasound scanner 32 communicates with the computer 22 and providesimage data to a data submodule 28 of the imaging software on thecomputer 22 The data submodule 28 orders the image data in an image dataarray, such that each ordered image property in the image data array hasassociated spatial coordinates. The x and y spatial coordinates aredetermined by the location of the data within the 250 by 250 frame,while the z spatial coordinate is assigned to the data by the datasubmodule 28 based on the frame in which the data is found,

In order to form three dimensional images based on the image datareceived from the ultrasound scanner 32, the computer 22 includes aconventional coordinate space modeling submodule 34 for generating acoordinate space. Preferably, the coordinate space takes the form of aright-angled parallelepiped, which will be referred to as modelPoly(where “poly” is an abbreviation of “polyhedron”) The modelPoly isdefined around the origin of a left-handed xyz coordinate system.

The coordinate space modeling submodule 34 handles all of the geometryinvolved in manipulating modelPoly in order to select perspectives fromwhich to view modelPoly. These geometric transformations are more easilyperformed when modelPoly remains located about the origin Accordingly,modelPoly is Geometrically transformed to form a winPoly, and it iswinPoly that is projected on the screen of the monitor 24 that the usersees.

The two dimensional views of winPoly shown on the screen of the monitor24 can be rendered using a number of different approaches. In the caseof three dimensional texture mapping, a surface of winPoly can begenerated by slicing through winPoly at a defined location andorientation to provide the desired cross-sectional view. A selectedsurface can also be viewed by displaying the intersection of a series ofparallel rays at a specified orientation with a predefined surface thatcan be defined by means of an equation. Alternatively, maximum intensityprojection (MIP) can be used to render a two dimensional view of winPolyby taking the intersection of a series of parallel rays of a selectedorientation with the pixel of maximum intensity that lies in the path ofsuch ray. Other well known rendering techniques include opacityrendering and surface rendering.

The selected surface of winPoly is projected to a two dimensional imageby lines that connect adjacent coordinates. The two-dimensionalprojection of winPoly is then sent to a raster submodule 38 (FIG. 1).The raster submodule 38 maps image data onto the two dimensional imageof each visible face of winPoly, by, for each ordered image property ofthe image data array that has associated coordinates on a visiblesurface, mapping such ordered image property onto such associatedcoordinates. First, the projected face is broken up into contiguous, 2dimensional triangles. Next, each triangle is filled by firstidentifying the minimum y value and the maximum y value that lie in thetriangle. Then, for these two points, and for each y value fallingbetween these two points, a line segment is determined. One end of thisline segment is a point having the smallest x integer value fallinginside the triangle, while the other end is a point having the largest xinteger value falling inside the triangle. The ordered image propertieshaving associated spatial coordinates corresponding to this line segmentare then mapped onto the line segment by the raster submodule.

The projected two dimensional image of winPoly is projected onto thescreen of the monitor where it can be seen by the user. Using the inputdevice 30, the user can send commands to an user interface submodule 40,where these commands are interpreted and transmitted to a coordinatespace modeling submodule 34. Examples of possible commands include thecommand to rotate, translate or scale winPoly. All of these commands,will result in a new view being displayed on the screen of the monitor24.

Moving from view to view within the series of views provided on themonitor 24 may also occur as a result of new data being communicated tothe data submodule 28. Specifically, consider the case in which asonographer is scanning an object of interest such as a patient'sforearm. When the sonographer begins the scan, the data submodule 28will not include very much image data regarding the patient's forearm.This paucity of information will be reflected in the monitor 24, whereonly a small portion of the forearm being scanned will be shown. Saythat the view selected of The forearm is an oblique view relative to theplane of the scan. Accordingly, as new data is obtained by theultrasound scanner 32 and is sent to the data submodule 28, the threedimensional image of the forearm modeled in the coordinate spacemodeling submodule 34 will grow, and the new image coordinates generatedby the new image data will replace, in some instances, image data thathad previously been acquired by the ultrasound scanner, in the sensethat this new image data will be displayed on the monitor 24 and willcover some of the image data that had previously been shown on themonitor 24.

Depending on the view selected, a view may change only slightly from theimmediately preceding view. For example, where the view selected is atexture mapping, showing both a plane parallel to the direction of thescan (i.e. a plane that corresponds to a single frame of data capturedby the ultrasound scanner 32), and a plane that is perpendicular to thedirection of the scan, the parallel surface shown in the monitor 24 willchange from view to view, in that different image coordinates arc beingprojected on the display coordinates of the monitor 24, and beingtexture mapped by the raster submodule 38 using newly available datafrom the data submodule 28. The portion of the previous view that was ona plane parallel to the direction of the scan will be “covered” by thenew data, in that the new data will be mapped to coordinates that form anew surface above the previously viewed surface. On the other hand, allof the image coordinates corresponding to the planar surface that isperpendicular to the direction of the scan, will be retained. This planewill simply increase in length, as additional image data is added.

Similarly, where a maximum intensity projection rendering method isused, whenever new image data becomes available, this data will becompared with the previously available image data. Only where the newlyacquired image data has the maximum intensity along the particularselected rays, will the new acquired image data replace the old imagedata previously projected onto the monitor.

The fact that from view to view many of the display coordinates of themonitor continue to show the same image coordinates provides anopportunity to reduce the data processing required to render a new viewof the data set. This is particularly true, where, as with realtimerendering of a static view of a dynamic image data set representing athree dimensional image, it is the data set that is changing. In suchcases, many of the display coordinates will continue to display the sameimage coordinates through a sequence of different views.

Specifically, using previous rendering techniques, once new data isacquired, all of winPoly is rendered. In the present invention, aftereach new frame of data is captured, only the small region in winPolythat is affected by the new data is rendered. The rest of winPoly hasalready been rendered, is unaffected by the new data, and need not berendered again.

In order to provide this feature, the computer 22 includes a selectionsubmodule 36. Whenever new data is acquired, and the view of winPolyshown on the monitor 24 changes, the selection submodule 36 considerseach of the display coordinates. Where such display coordinate continuesto show the same winPoly coordinate or image coordinate, the selectionsubmodule 36 will bypass the raster submodule 38 with respect to suchdisplay coordinate and the projection submodule 42 will continue toproject the image coordinate onto such display coordinate. On the otherhand, if the selection submodule 36 determines that the displaycoordinate now shows a new winPoly coordinate or image coordinate, thenthe raster submodule 38 will not be bypassed; instead, such displaycoordinate will again be rasterized.

Referring to FIG. 2, a code logic listing shows the steps of a selectiverendering method for rapid three dimensional imaging in accordance withthe preferred aspect of the invention where new frames of image data arecontinually being added. This method is preferably implemented using theabove-described selective rendering system.

When scanning a patient, an ultrasound operator generates a sequence offrames of image data by passing a probe over part of a patient. Asdiscussed above, each stored frame consists of about 250 by 250 pixels,and the ordering of the image data can be represented spatially usingspatial coordinates. The corresponding X and Y spatial coordinates aredetermined by the location of the data within this 250 by 250 frame. TheZ spatial coordinate is assigned to the data based on the frame in whichthe data is located.

During the scan, the image data is periodically increased by a new framebeing added. This additional frame is designated as a Z frame, becauseall of the data coordinates in this frame are assigned a common Zcoordinate reflecting the fact that they all lie in a common frame.

In realtime three dimensional rendering, a view of winPoly is typicallybeing shown on the monitor when the new image data is received. The caseof texture mapping was discussed above in connection with the system ofFIG. 1. The logic code of FIG. 2 relates to volume rendering, ratherthan surface rendering, and a 3-tuple ray, rayWin, is used forrendering.

For each point pWin in the view of winPoly, raywin extends in thedirection (0,0,1) from pWin. In other words, rayWin extends parallel tothe normal of the screen. The point pWin in the view of winPolycorresponds to a point pData in the image data. Due to thecorrespondence between the image data and winPoly (the image data has aone-to-one mapping onto the coordinates of modelPoly, which isgeometrically manipulated to yield winPoly), rayWin corresponds to a3-tuple directed line segment rayData, which begins at the point pData.

Volume rendering involves moving along rayData in steps of a fixedincrement, and choosing all points on the ray that are spaced apart bythis fixed increment. Based on the image data, a final intensity isdetermined and is then displayed at the point pWin on the monitor. Thenature of the determination performed will depend on the type ofrendering. In the case of maximum intensity projection, this willinvolve determining which point along the ray is of maximum intensity,and displaying this maximum intensity.

The first optimization step involves determining whether or not rayDatapasses through the new Z frame at all. In other words, it involves, foreach point pWin on the surface being displayed on the monitor,determining whether a ray passing through such point also passes throughthe new Z frame (called WEDGE_DATA in FIG. 2).

The intersection of the new Z frame and rayData can readily bedetermined as the equation of both rayData and the new Z frame areknown. This optimization step is performed by the functionrayintersectsWedge( ), which accepts as an argument the points on thescreen, and which is true when the ray from such point intersects thenew Z frame, and is otherwise false. If this function yields the resultfalse, then no new rendering need be provided along such ray. On theother hand, if this function yields the answer true, it is stillpossible to limit the amount of rendering required using the secondoptimization step.

If rayData does intersect the new Z frame, then an intersection segmentof rayData is determined with end points rayBegin and rayEnd. Then, onlythe points that lie on rayData between rayBegin and rayEnd need berendered, the remainder of the points on rayData can be ignored.

It will be apparent that the present invention may be implemented inother specific forms without departing from the spirit or centralcharacteristics thereof. In particular, while the invention has beendescribed in the context of medical co-imaging generally, and ultrasoundimaging in particular, it will be apparent to those skilled in the artthat the invention is applicable in other imaging contexts as well. Thepresently discussed embodiments are considered to be illustrative andnot restrictive, the scope of the invention being indicated by theappended claims rather than the foregoing description, and all changesthat come within the meaning and range of the claims are thereforeintended to be embraced.

What is claimed is:
 1. A method for updating a display from an n^(th)view of a series of views of a three dimensional image to an (n+1)^(th)view of the series of views of the three dimensional image, the threedimensional image being generated in an image coordinate set of acoordinate space, each image coordinate in the image coordinate sethaving an associated image property, and the image coordinate setincluding, for the n^(th) view of the series of views, an associatedn^(th) image coordinate subset; the display having a display coordinateset, the display coordinate set having, for the n^(th) view of theseries of views, an associated n^(th) display coordinate subset, and then^(th) view of the series of views being generated by projecting theassociated n^(th) image coordinate subset onto the n^(th) displaycoordinate subset on the display so that each display coordinate in then^(th) display coordinate subset has an associated n^(th) view-specificimage coordinate projected thereon; the (n+1)^(th) view of the series ofviews being generated by projecting the associated (n+1)^(th) imagecoordinate subset onto the (n+1)^(th) display coordinate subset on thedisplay so that each display coordinate in the (n+1)^(th) displaycoordinate subset has an associated (n+1)^(th) view-specific imagecoordinate projected thereon; the method comprising for each displaycoordinate in both the n^(th) display coordinate subset and the(n+1)^(th) display coordinate subset, determining whether the n^(th)view-specific image coordinate is the same as the (n+1)^(th)view-specific image coordinate; and, when the n^(th) view-specific imagecoordinate is the same as the (n+1)^(th) view-specific image coordinate,retaining the projection of the n^(th) view-specific image coordinateonto such display coordinate as the projection of the (n+1)^(th)view-specific image coordinate onto such display coordinate; and, whenthe n^(th) view associated image coordinate is different from the(n+1)^(th) view associated image coordinate, projecting the (n+1)^(th)view associated image coordinate onto such display coordinate.
 2. Themethod as defined in claim 1 wherein; in an incremental time between thedisplay of the n^(th) view of the series of views and the (n+1)^(th)view of the series of views of the three dimensional image, the imagecoordinate set of the coordinate space increases as an additional imagecoordinate subset is added to the image coordinate set; and the(n+1)^(th) view specific subset of the image coordinate set intersectswith the additional image coordinate subset.
 3. The method as defined inclaim 2 wherein the three dimensional image is being generated in realtime by scanning an imaged object.
 4. The method as defined in claim 1wherein the image coordinate set is fixed and the (n+1)^(th) view of theseries of views is generated by selecting the (n+1)^(th) view-specificsubset of the image coordinate set.
 5. A method of updating a displayfrom a preceding view in two successive views in a series of views of athree dimensional image to a subsequent view in the two successive viewsin the series of views of the three dimensional image, the threedimensional image being generated in an image coordinate set of acoordinate space, each image coordinate in the image coordinate sethaving an associated image property; the display having a displaycoordinate set; the preceding view being generated by a precedingprojection of a preceding view image coordinate subset of the imagecoordinate set onto a preceding view display coordinate subset of thedisplay coordinate set so that each display coordinate in the precedingview image coordinate subset has an associated preceding view imagecoordinate in the preceding view image coordinate subset projectedthereon; the subsequent view being generated by a subsequent projectionof a subsequent view image coordinate subset of the image coordinate setonto a subsequent view display coordinate subset of the displaycoordinate set so that each display coordinate in the subsequent viewimage coordinate subset has an associated subsequent view imagecoordinate in the subsequent view image coordinate subset projectedthereon, the method comprising for each display coordinate in both thepreceding view display coordinate subset and the subsequent view displaycoordinate subset, determining whether the associated preceding viewimage coordinate is the associated subsequent view image coordinate;when the associated preceding view image coordinate is the associatedsubsequent view image coordinate, retaining the preceding projection ofthe associated preceding view image coordinate onto such displaycoordinate as the subsequent projection of the associated subsequentview image coordinate onto such display coordinate; when the associatedpreceding view image coordinate is not the associated subsequent viewimage coordinate, stopping the preceding projection of the associatedpreceding view image coordinate onto such display coordinate andbeginning the subsequent projection of the associated subsequent viewimage coordinate onto such display coordinate.
 6. The method as definedin claim 5 wherein the two successive views in the series of views ofthe three dimensional image are any two successive views in the seriesof views of the three dimensional image.
 7. The method as defined inclaim 5 wherein in an incremental time between the display of thepreceding view and the subsequent view, the image coordinate set of thecoordinate space increases as an additional image coordinate subset isadded to the image coordinate set; and the subsequent view subset of theimage coordinate set intersects with the additional image coordinatesubset.
 8. The method as defined in claim 7 wherein the threedimensional image is being generated in real time by scanning an imagedobject.
 9. The method as defined in claim 5 wherein the image coordinateset is static and the subsequent view subset is selected from the staticimage coordinate set.
 10. A system for updating a display from apreceding view in two successive views in a series of views of a threedimensional image to a subsequent view in the two successive views inthe series of views of the three dimensional image, the threedimensional image being generated in an image coordinate set of acoordinate space, each image coordinate in the image coordinate sethaving an associated image property; the display having a displaycoordinate set; the preceding view being generated by a precedingprojection of a preceding view image coordinate subset of the imagecoordinate set onto a preceding view display coordinate subset of thedisplay coordinate set so that each display coordinate in the precedingview image coordinate subset has an associated preceding view imagecoordinate in the preceding view image coordinate subset projectedthereon; the subsequent view being generated by a subsequent projectionof a subsequent view image coordinate subset of the image coordinate setonto a subsequent view display coordinate subset of the displaycoordinate set so that each display coordinate in the subsequent viewimage coordinate subset has an associated subsequent view imagecoordinate in the subsequent view image coordinate subset projectedthereon; the system comprising a determining means, a retaining meansand a stopping means wherein for each display coordinate in both thepreceding view display coordinate subset and the subsequent view displaycoordinate subset, said determining means determines whether theassociated preceding view image coordinate is the associated subsequentview image coordinate; when the associated preceding view imagecoordinate is the associated subsequent view image coordinate, saidretaining means retains the preceding projection of the associatedpreceding view image coordinate onto such display coordinate as thesubsequent projection of the associated subsequent view image coordinateonto such display coordinate; when the associated preceding view imagecoordinate is not the associated subsequent view image coordinate, saidstopping means stops the preceding projection of the associatedpreceding view image coordinate onto such display coordinate andbeginning the subsequent projection of the associated subsequent viewimage coordinate onto such display coordinate.
 11. The system as definedin claim 10 wherein the two successive views in the series of views ofthe three dimensional image are any two successive views in the seriesof views of the three dimensional image.
 12. The system as defined inclaim 10 wherein in an incremental time between the display of thepreceding view and the subsequent view, a data update means forincreasing the image coordinate set of the coordinate space by adding anadditional image coordinate subset to the image coordinate set; and thesubsequent view subset of the image coordinate set intersects with theadditional image coordinate subset.
 13. The system as defined in claim12 further comprising scanning means for generating the threedimensional image by scanning an imaged object.
 14. The system asdefined in claim 10 wherein the image coordinate set is static and thesubsequent view subset is selected from the static image coordinate set.